As seen in a video of their magical visit, the famous Brits were first shown onto the set of the Gryffindor Common Room in Hogwarts, used by Harry Potter (Daniel Radcliffe) and his housemates in most of the eight blockbuster films. There, the six-months-pregnant Duchess of Cambridge, 31 — her bump prominently displayed in a polka-dot Topshop dress and Ralph Lauren blazer — joined her husband and tour instructor Scott Heron for a lesson in "spell techniques." (The Duke's younger brother, 28, was otherwise engaged at the Weasley's house, where he seemed fascinated by a magic knife and ironing board.)

"They were great. They picked it up really quickly," Heron said of the soon-to-be first-time parents' wand technique. "I was very impressed."

Later, Prince Harry met up with his brother and sister-in-law on the Diagon Alley set, where each was given a light-up wand. The group was then instructed to point their wands at a sign in the shape of a cauldron and press a button hidden in the base of their props to make it explode. (See them practice the move in the video above!)

Prince Harry, Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge laugh as they hold wands on the set used to depict Diagon Alley in the Harry Potter Films during the Inauguration Of Warner Bros. Studios Leavesden on April 26, 2013 in London, England.Chris Jackson/Getty Images

"It's not fair — they've had a lesson!" Harry said of William and his wife. And in fact the lesson paid off: Harry couldn't get his wand to work, but the royal couple pulled off the trick with ease. "It's always the wizard, never the wand," instructor Lauren Coates joked of the younger Prince.

"Harry's just excited to see a real-life talking owl in the Harry Potter studios," William said later, after the trio had moved on to the Batman exhibit. "I haven't told him yet that Harry Potter is fictional, so please keep the secret for a little longer."